Senator Marco Rubio is widely expected to announce his campaign on Monday, and ex-Florida governor Jeb Bush is actively considering a run.

With little serious competition on the Democratic side, she immediately becomes the frontrunner for her party's nomination.

She also said in the video that she will soon be "hitting the road to earn your vote."

Presumptive campaign chairman John Podesta told donors and other backers in Sunday emails that Clinton's first campaign stops will be in Iowa -- the state that votes first in the primary process early next year to decide the parties' nominees -- and that "a formal kickoff event" will be held next month.